The wireless communications network has grown exponentially over the years. A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simplified network architecture. LTE systems, also known as the 4G system, also provide seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNodeBs or eNBs) communicating with a plurality of mobile stations, referred to as user equipments (UEs). The 3rd generation partner project (3GPP) network normally includes a hybrid of 2G/3G/4G systems. The Next Generation Mobile Network (NGMN) board, has decided to focus the future NGMN activities on defining the end-to-end requirements for 5G new radio (NR) systems.
Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ) are key measurements of signal level and quality for LTE and NR networks. In cellular networks, when UE moves from cell to cell and performs cell selection, reselection and handover, UE needs to measure the signal strength and quality of the neighbor cells. Received Strength Signal Indicator (RSSI) measurements can be used to determine RSRP and RSRQ. RSSI measures the average total received power observed in OFDM symbols containing reference symbols in the measurement bandwidth over certain resource blocks. RSSI is measured over the entire bandwidth including noise, serving cell power and interference power.
In NR systems, UE can be configured to measure synchronization signal (SS) blocks (SSB) and/or channel state information (CSI) reference signal (CSI-RS). Since RSSI measurement can be used to derive SS-RSRP and SS-RSRQ, sometimes RSSI is referred to as NR carrier RSSI or SS-RSSI. For SS-RSSI measurement, a set of time slots and OFDM symbols for SS-RSSI time-domain measurement resource can be explicitly configured per frequency carrier for a UE in RRC_CONNECTED mode and in RRC_IDLE mode. The time slots for RSSI measurement resource are configured by a bitmap with each bit corresponding to each slot of the slots within the SSB measurement time configuration (SMTC) window duration. OFDM symbols level configuration for the configured slots is achieved via configuring a limited set of ending symbols, and the set of symbols in a slot for RSSI measurement resource is from symbol 0 to the ending symbol. The time duration TRSSI for the by-default RSSI measurements is defined as follows: TRSSI=configured SMTC measurement window if measurement gap is not used; or TRSSI=overlapped time span between configured SMTC measurement window and minimum measurement time within measurement gap if measurement gap is used.
The cell-specific timing for RSSI measurement will involve frame boundary and slot boundary detection, and it will introduce more UE complexity due to reading the physical broadcast channel (PBCH). For carrier-specific RSSI measurement, the configured slots and symbols are aimed to avoid uplink symbols for time division duplex (TDD) case. It is reasonable to assume certain level of synchronization between cells with the configured slots and symbols for RSSI measurement.